Presentation on theme: "What is a mineral? A mineral is a (1)naturally occurring (2)inorganic, (3)solid with a (4)definite chemical composition and (5)crystalline structure. There."— Presentation transcript:
What is a mineral? A mineral is a (1)naturally occurring (2)inorganic, (3)solid with a (4)definite chemical composition and (5)crystalline structure. There are over 4000 known minerals, but only about 20 are common.
What is a mineral? (cont.) Minerals can either be a made of a pure substance – a single element (gold, silver, lead, iron) BUT Most minerals are compounds The same elements are found in most minerals – they are called mineral forming elements: –Oxygen; Silicon; Aluminum; Iron; Calcium; Sodium; Potassium; Magnesium
How do minerals form? Minerals can form several ways: 1.From molten rock/magma 2.Due to intense heat and pressure 3.Evaporation 4.Chemical Action
What are silicates? Minerals are classified into 2-groups based on their composition: 1.Silicate Minerals 2.Nonsilicate Minerals
Silicate Minerals Are minerals made of the 2 most abundant elements in Earth’s crust – silicon (Si) and oxygen (O) A silicate may also contain one or more metallic elements like aluminum or iron There are a few silicates that do not contain metals – like quartz More that 90% of the minerals in Earth’s crust are silicates Examples – feldspars, quartz, hornblende, olivine, muscovite, biotite
Nonsilicate Minerals Groups 1.Carbonates – metal + C + O 2.Halides – metal + halogen 3.Native elements – single element 4.Oxides – Metal + O 5.Sulfates – S + metal + O 6.Sulfides – S + metal
How To Identify Minerals Based on Properties
quartz selenium calcite quartz Color
First thing noticed Not useful property to identify minerals because: –One mineral can have different colors –Different minerals can have the same color However some minerals do have a distinct color. Examples: sulfur, malachite, cinnabar.
Crystal Shape Arrangement of its component atoms and/or ions Responsible for the outward shape of the crystal Crystal system affects a number of other properties such as cleavage, density, and hardness
Luster The way light reflects off the surface of a mineral How you would tell someone how a mineral looks Nothing to do with color or shape Terms used are generally not scientific, but are meant to be descriptive
Hardness A good physical property in mineral identification Measure of the strength of the structure of the mineral relative to the strength of its chemical bonds --- Stronger bonds = greater hardness Hardness can be tested through scratching A mineral can only be scratched by a harder substance
Streak Color of the powder of a mineral To test for streak, rub a mineral across a tile of white unglazed porcelain and examine the color of the "streak" left behind Two minerals that have similar outward color may have different colors when powdered. hematite galena
Cleavage Cleavage is a smooth break producing what appears to be a flat crystal surface that can be broken along the same parallel plane over and over again Terms are: perfect, imperfect, good, distinct, indistinct, and poor. biotite
Fracture is a description of the way a mineral tends to break The surface that can be described as Smooth, Irregular, Jagged, Splintery Most common fracture type is conchoidal which is a smoothly curved fracture that looks like broken glass Fracture
Specific Gravity Compares the density of a mineral to the density of water If a mineral has a SG of 2, then it is twice as dense as water If a mineral has a SG of 3 then it is three times as dense as water and so forth.
Additional Mineral Properties
Acid Test Carbonate minerals (calcite & dolomite) tend to react to acids The reaction is written as follows for calcite, the mineral for which this test is made famous:calcite CaCO 3 + 2H (+1) -------> Ca (+2) + H 2 O + CO 2 (gas)
The Fluorescence Minerals Light from these ultraviolet lamps reacts with the chemicals of a mineral and causes the mineral to glow; this is called fluorescence. Examples: Fluorite Calcite Autunite Willimite
Magnetism Magnetite is a natural magnet, which is a good way to identify it from other metallic mineral ores.
T aste Most commonly "tasted" mineral is halite/rock salt YOU should never do this because there are minerals that are poisonous Some solubility in water is required in order to have a taste
The Scent of a Mineral The most renowned smelly mineral is sulfursulfur Marcasite gives off a noticeable sulfur-like odor when it decomposesarcasite Arsenic minerals tend to have a garlic scent as is consistent with the element and poison arsenic arsenic Clay minerals have a clay-like smell that is sometimes called earthylay